1. Field of the Invention
The invention relates generally to a caster adjustment apparatus and, more particularly, to a caster adjustment apparatus for use in a steerable axle assembly, of either the driven or non-driven type, of a motor vehicle.
2. Related Art
Motor vehicles may employ a solid, steerable front axle arrangement in which a yoke is fixedly attached to the solid axle and a steering knuckle is pivotally attached to the yoke via a single shaft, or kingpin, or alternatively by spaced apart ball joints. Alternatively, in the case of a driven, steerable front axle arrangement, the yoke may be fixedly attached to an axle housing surrounding the driving axle shaft. In either case, the steering knuckle is coupled with the spindle upon which the vehicle wheel is mounted for rotation. In response to control forces, the steering knuckle pivots relative to the yoke and axle to provide steering at the wheels. Caster and camber adjustments are critical to proper road handling and tire wear. Caster is the angle, in a side elevational view of the vehicle, between the steering, or kingpin axis and the vertical. Caster angle is important in vehicle suspensions because it is the caster adjustment which provides part of the tendency of the vehicles' wheels to return to a straight ahead position following negotiation of a curve. Limited means have been available previously to adjust caster. Limited caster correction can be achieved by placing shims between the axle and leaf springs. While such an approach may be effective if both wheels require equal correction for caster, the shimming approach has been shown to be ineffective and undesirable due to the need of twisting the relatively stiff axle. Additionally, while ball joints permit an initial setting of caster, they are difficult to disassemble and are typically not reusable. Accordingly, ball joints do not provide a viable option for subsequent caster adjustment after initial assembly. Subsequent devices, comprising kingpins in conjunction with one or more eccentric bushings, have been used in an attempt to overcome the limitations of prior devices.
Automotive design engineers continue to search for a simple, cost-effective, and reusable means for providing caster adjustment in steerable axle assemblies.